This invention relates to an article surveillance security system with self-alarm to be attached to articles or goods so that they can be protected against shoplifting in a common retail shop, etc.
A conventional article surveillance security system contains a passive paper tag without a built-in power supply. The paper tag is attached to articles or goods, reacts and sounds an alarm at an entrance gate when it is taken out of a retail shop without permission, that is to say when it is passing by a transmitter mounted at an entrance gate, etc. of the shop, Thereby it protects the articles or goods against shoplifting. Although a passive paper tag is cheap in cost, it cannot correctly distinguish the shoplifter when a plurality of shoppers simultaneously pass by the gate. Therefore, it is hard to catch the shoplifter in flagrante delicto. In addition, if a shoplifter tries to run away from the alarm, a shopman cannot successfully catch the shoplifter because the shopman cannot immediately locate the paper tag by which an alarm is sounded.
The above described problem has been solved by an article surveillance security system with self-alarm which contains a power supply, and makes a tag itself sounding an alarm when it receives an radio wave from a transmitter mounted at an entrance gate of a shop. For example, in the case of a CD(compact disk), the article surveillance security system with self-alarm of this type is provided with a clear case 9 made of synthetic resin, a circuit substrate 10, an alarm operation switch 11, and a buzzer 12 as shown in FIG. 11. The clear case 9 contains a cassette 8 storing a CD(compact disk). The buzzer 12 is controlled by the circuit substrate 10 and the alarm operation switch 11. If the cassette 8 does not exist in the clear case 9, then the alarm operation switch 11 sounds the buzzer. Otherwise, if the article surveillance security system with self-alarm passes through the gate, the circuit sounds the buzzer. In a shop, the cassette 8 containing a CD (compact disk) is put in the clear case 9 with the article surveillance security system with self-alarm, and displayed. When a salesperson sells the CD to a shopper, the salesperson first sets the buzzer 12 in an inactive state, then takes the cassette 8 out of the clear case 9, and delivers the CD to the shopper in exchange for charge. The article surveillance security system with self-alarm can be repeatedly used after the cassette 8 has been taken out.
In the above described article surveillance security system with self-alarm, when a shopper takes out the cassette 8 illegally from the clear case 9 with the article surveillance security system with self-alarm, the alarm operation switch 11 detects the absence of the cassette 8 in the clear case 9 and issues an alarm instruction to the buzzer 12 to make it sounding upon receipt of the alarm instruction. Thus, a salesperson can be informed that the cassette 8 has been illegally taken out of the clear case 9. In addition, if a shopper tries to take out a cassette 8 contained in a clear case 9 with an article surveillance security system with self-alarm as it is, the receiving circuit of the article surveillance security system with self-alarm receives a signal from a transmitting circuit provided at the entrance gate, etc., and issues an alarm instruction to the buzzer 12. The buzzer 12 receives the alarm instruction and sounds. Thus, the salesperson can be informed that the compact disc is being illegally taken out of the shop.
Furthermore, as shown in FIG. 12, a tag 15 of an article surveillance security system can also be individually attached to articles or goods by using a tape, etc. in other embodiment. This type of tag has been already suggested by the same applicant. The above described case also contains the circuit of the article surveillance security system with self-alarm. In FIG. 12, 16 is a LED(light emission diode).
FIG. 13 is a detailed analytic view of FIG. 12. FIG. 13(a) is a view from the bottom of a tag case 15 shown in FIG. 12. FIG. 13(b) is a view of the printed substrate contained in the tag case, when it is taken out of the tag case. FIG. 13(c) is a view of FIG. 13(a) without the bottom plate.
In FIG. 13(c), 31 is a display window of the LED(light emission diode) corresponding to the LED(light emission diode) 16 shown in FIG. 12. In FIG. 13(c), there are a plastic case 18, which has a shape of a turned boat as shown in FIG. 12, a printed substrate 19 stored in the case, a buzzer 20, a battery 21 , a long hole 22 made in the printed substrate, a switch 23, a male lock material 24, a female lock material 25, a lock pin 26, a bottom plate 27, a snap switch 28, a hole 29 in the bottom plate, and an actuating chip 30 of the snap switch 28. The above described self-alarm tag case has the shape of a turned boat of 9 cm long and 2 cm wide. The actuating chip 30 of the snap switch 28 projected from the hole in the bottom plate 29 of the case is pressed against articles or goods, and is fixed to the articles or goods by using a tape, etc. In this type of tag, the buzzer does not sound while the actuating chip is pressed against articles or goods. However, if the tag is illegally removed from the articles or goods, the operation chip 30 is turned ON, and accordingly the buzzer sounds. Additionally, in this type of tag, if articles or goods is illegally taken out of the entrance gate without permission before releasing a lock, the tag receives a radio wave from the transmitter provided at the entrance gate, thereby sounding the buzzer.
Since articles or goods sound an alarm by itself by using the article surveillance security system with self-alarm, the shoplifter can be easily specified, and the shoplifter can be more effectively caught in flagrant than using the above described passive paper tag. However, the paper tag is 10 through 60 yen apiece while the self-alarm tag is 400 through 600 yen apiece. Therefore, the self-alarm tag is much more expensive, and is hard to be used in large quantities. The paper tag is commonly a bar code printed paper containing a printed tuning circuit comprising LC, which is operated at a frequency of 8.2 MHz. A frequency of 8.2 MHz is appropriate for the above described LC to be made in size of 2 through 3 cm in length and width. Another paper tag operated at a frequency of 58 KHz has also become popular. The above described LC circuit at 58 KHz is too large to be practical, and the paper tag at 58 KHz uses a special capacitor. In general, a higher-quality function can be obtained at a low frequency of 58 KHz. However, since a generally used LC circuit can be adapted at a frequency of 8.2 MHz, the paper tag at 8.2 MHz is more costly.
The above described self-alarm tag is already known to be operated at frequencies 22 KHz, 37.5 KHz, and 31.5 KHz. However, if the self-alarm tag is operated at the same frequency as that of the above described passive paper tag, then the transmitter for the paper tag can be used simultaneously for the self-alarm tag as it is. Therefore, both type of tags can be easily used in the passive paper tag system which has been widely used. That is, the expensive self-alarm tag has a strong effect for protecting articles or goods against shoplifting only by using even one in ten tags. Accordingly, if the passive paper tag and self-alarm tag can be commonly used at the same frequency, then the transmitter provided at the entrance gate, etc. of a shop can also be commonly used, thereby contributing to be popularized.
That is, it is desired that the above described self-alarm tag is designed for 58 KHz or 8.2 MHz which is the common frequency with that of the paper tag. However, the radio wave emitted from the transmitter has a very low power emission of radio wave according to the rule of the Radio Wave Law, and the power supply is a small lithium ion battery (3V) which should work for about 4 years as a useful tag. Therefore, the operating current in a tag circuit should be 1 or 2 xcexcA. As a result, a tag at the frequency of 58 KHz can be barely realized, but it is difficult to design a tag at the frequency of 8.2 MHz, and no practical products have been successfully realized.
That is, although it is necessary to reduce an operating current flowing through a transistor such as 1 or 2 xcexcA by setting the load resistance at a high value of 3 through 5 Mxcexa9. However, with the above described settings, the operating current becomes too low, and a transistor cannot sufficiently amplify the signal at the frequency of 8.2 MHz. Simultaneously, as the impedance becomes high through the high load resistance, thereby it easily generates noise.
Furthermore, when an operating point moves even slightly by the fluctuation of an environmental temperature, it is difficult to keep a stable operation of the circuit because of the original tight design.
On the other hand, the self-alarm tag operating at a frequency of 58 KHz is a useful tag, but the passive paper tags operating at a frequency of 58 KHz and the passive paper tags operating at a frequency of 8.2 MHz occupy an equal market share. Therefore, as a shop already provided with the 8.2 MHz passive tag system does not require additional equipment investment if it adopts the 8.2 MHz self-alarm tag, there is a strong demand for the 8.2 MHz self-alarm tag.
However, although there have been a number of developments for the above described self-alarm tag, the above described problems have not been solved at a frequency of 8.2 MHz, and no successful products have been disclosed yet. Under the circumstance, this invention has been developed to generate an effective receiving circuit, specifically to successfully develop an self-alarm tag stably operating at a frequency of 8.2 MHz.
The object of this invention is to provide a receiving circuit of an article surveillance security system with self-alarm or a self-alarm tag which has a power supply of approximately four-year durability, and stably operates with a very low level radio wave at a conventionally inapplicable frequency band (for example, 8.2 MHz).
In addition, the object of the invention is providing a receiving circuit of an article surveillance security system with self-alarm or a self-alarm tag having a power supply of approximately four-year durability, stably operating with a very low level radio wave at a conventionally inapplicable frequency band (for example, 8.2 MHz), and suppressing external noise, especially due to a malfunction at a frequency band used in a mobile telephone.
The circuit of the article surveillance security system with self-alarm according to this invention sets from 6 through 10 MHz as a central frequency, receives a low level radio wave swept within xc2x15 through 15% from the central frequency, and sounds the alarm. It includes a tuning circuit tuning to the central frequency, and a differential amplifier for amplifying and detecting an output signal of the tuning circuit. The load resistance of the differential amplifier is set to from 3 through 5 Mxcexa9, and the operating current of the differential amplifier is set to 3 xcexcA or less. The base-emitter of the amplification/detection transistor (Tr1) of the differential amplifier are connected to the base-emitter of another diode-connected transistor (Tr2) of the differential amplifier in order to stabilize a circuit operation against a bias drift by temperature.
Furthermore, the output of the differential amplifier is connected to a charge/discharge circuit including a resistor and a capacitor and a comparison circuit through a direct-coupled amplifier in series, and it is detected that receiving pulses corresponding to the sweep frequency have been supplied predetermined times, thereby removing the non-successive receiving noise around the central frequency. Otherwise, the output of the differential amplifier is supplied to a microcomputer through the direct-coupled amplifier after AD(analog-digital) conversion, and it is detected that receiving pulses corresponding to the sweep frequency have been supplied predetermined times, thereby removing the non-successive receiving noise around the central frequency.
In addition, the article surveillance security system with self-alarm according to this invention sets the central frequency of 6 through 10 MHz, and sounds the alarm when receiving a low level radio wave swept within the range of xc2x15 through 15% from the central frequency, and it includes a tuning circuit for the central frequency; an inductance inserted in series with the signal path having low impedance at the above described frequency of 6 through 10 MHz, and high impedance at 1 GHz or more; and a first stage amplifier having high load resistance for amplifying and detecting the output of the tuning circuit supplied through the inductance.
Furthermore, the 1005 size is used as a unit of the resistance, the impedance, etc of the above described circuit, so that the stray impedance at a frequency of 1 GHz or more in the input circuit, the bias circuit, and the load circuit of the differential amplifier can be as small as possible. The shield effect for external noise can be improved by widening an earth pattern and a pattern of the power supply line of the above described circuits on the printed substrate.
In addition, in this embodiment the first stage amplifier is a differential amplifier, and the load resistance of the differential amplifier is 3 through 5 Mxcexa9 so that the operating current of the differential amplifier can be 3 xcexcA or less, and the base-emitter of the amplification/detection transistor (Tr1) of the differential amplifier are connected to the base-emitter of another diode-connected transistor (Tr2) as a pair to the transistor (Tr1) of the differential amplifier to stabilize against bias drift by temperature. The output of the differential amplifier is connected to a charge/discharge circuit including a resistor and a capacitor and a comparison circuit through a direct-coupled amplifier, and it is detected that receiving pulses corresponding to the sweep frequency have been supplied predetermined times, thereby removing the non-successive receiving noise around the central frequency.
Otherwise, the output of the differential amplifier is supplied to a microcomputer through the direct-coupled amplifier after AD conversion, and the microcomputer detects that receiving pulses corresponding to the sweep frequency have been supplied predetermined times, thereby removing the non-successive receiving noise around the central frequency. In addition, the central frequency is 8.2 MHz, the sweep range can be xc2x110%, and the sweep frequency is 50 through 80 Hz.